1. Field of the Invention
The invention relates to a silica glass member for semiconductor such as a furnace core tube, a wafer boat and a heat insulating mould used for the production of a semiconductor and a production method thereof.
2. Description of the Related Art
Conventionally, as silica glass members for semiconductor of this kind, those comprising electrically melted quartz glass which is produced by melting a natural crystal in an electric furnace and then solidifying, those comprising an OH group (hydroxyl group)-containing soot remelted synthetic silica glass produced by hydrolyzing a silicon compound such as silicon tetrachloride in an oxyhydrogen flame and then melting or those comprising highly heat-resistant soot remelted synthetic silica produced by processing a porous body of a synthetic silica powder obtained by hydrolyzing a silicon compound such as silicon tetrachloride in an oxyhydrogen flame and deposited on a synthetic silica powder on a target, in reducing gas having a temperature as high as 1200° C. or more into a transparent glass, are known.
However, those comprising electrically melted quartz glass has a viscosity of 1013.2 poise at 1200° C. and exhibits high heat resistance. However, these materials have the drawback that the concentration of metal impurities in these materials is high, so that a lot of impurities is discharged and there is therefore a lot of contamination to a semiconductor wafer during the course of the process.
On the other hand, with regard to those comprising an OH group-containing soot remelted synthetic silica glass, high purity materials can be obtained in which each concentration of metal impurities, such as Fe (iron), Cu (copper), Cr (chromium) and Ni (nickel), which are harmful to a semiconductor is 10 ppb or less. However, because no treatment for dehydration of an OH group produced during the production of a porous silica body is carried out, an OH group is contained in the glass in an amount of 100 to 1000 ppm and the viscosity at a temperature of 1200° C. is 1012.7 poise. Therefore, at a temperature above 1100° C., a deformation due to viscosity is caused, giving rise to unacceptable phenomena such as an expansion of a furnace core tube and a distortion of a wafer boat, leading to a shortage of the life of a silica glass member for semiconductors resultantly.
Meanwhile, those comprising highly heat-resistant soot remelted synthetic silica glass have high purity with each concentration of Fe, Cu, Cr and Ni being 10 ppm or less like the base materials comprising an OH group-containing soot remelted synthetic silica glass, and contain 50 ppm or less of an OH group and a viscosity of 1013.1 poise at 1200° C. which are the same levels as those of the glass comprising electrically melted quartz glass. However, the development of higher quality glass materials is needed along with the development of more miniaturized and highly integrated semiconductor devices.